Troy Smith Posted February 17, 2019 Share Posted February 17, 2019 A suggestion, and it's just a guess, so please ignore if cobblers, but given the strength of rare earth magnets, how about either drilling a holes for one in each of the front wheels, or even just adding metal rods to them, and then mounting a magnet under the display area. You have already added weight, but this might be another added method to help even out the tail? Not seen this done, so very much an armchair bit of pondering? 3 Link to comment Share on other sites More sharing options...
Johnny_K Posted February 17, 2019 Share Posted February 17, 2019 That was a great explanation of how the length of the moment arm affects the amount of required weight. How are you going to remove weight from that tail of the plane? 2 Link to comment Share on other sites More sharing options...
Jamie @ Sovereign Hobbies Posted February 17, 2019 Author Share Posted February 17, 2019 On 2/17/2019 at 8:07 PM, Nikolay Polyakov said: But not so much loss of the weight when you cut it a half, right? You have done a very interesting calculations here, bravo! What about to put a some weight into the forward tunnel part (I think it’s not be visible there)? Cheers! 🙂 Exactly - those tongues can be drilled out so they still function, but it saves a little weight. Not much, but as the maths shows, every little bit saved at the back saves twice as much (or more) weight needed at the front The suggestion to fill the front half of the crew access tunnel is good - I hadn't thought of that! On 2/17/2019 at 8:08 PM, Troy Smith said: A suggestion, and it's just a guess, so please ignore if cobblers, but given the strength of rare earth magnets, how about either drilling a holes for one in each of the front wheels, or even just adding metal rods to them, and then mounting a magnet under the display area. You have already added weight, but this might be another added method to help even out the tail? Not seen this done, so very much an armchair bit of pondering? It's probably not a bad shout Troy, and I happen to have some from the r/c world again as they are popular for holding hatches on etc. If needs be, I'll do it On 2/17/2019 at 8:15 PM, Johnny_K said: That was a great explanation of how the length of the moment arm affects the amount of required weight. How are you going to remove weight from that tail of the plane? Plan A was to use a rotary tool and sanding bit: ...but it's broken. Thinking back, I think I burned it out 4 years ago working the valve ports on my MG Midget cylinder head. Plan B is to use a power drill and flap wheel which works, but the battery needs charged. I've drilled out holes in one of the tailplane (horizontal stabilizer) tongues and I've got a little bit of thinning on one half done. I'll get more done with a recharge... Each half of the tailplane (one side, upper and lower parts together) weighed 19.3g before any fettling. In the state above (one piece partly thinned, the other not touched) the total weight is down to 18.3g. As per the previous post, that's >2g of nose weight saved already and the total weight on the mainwheels reduced by 3g (compared to a noseweight-only solution). There won't be any silver bullets here, but working away at the whole back end will see lots of small weight savings which will add up to considerable amount. Whether it's enough remains to be seen! Fullsize aircraft sometimes use a weight and balance sheet with lots of component masses positioned relative to a datum point. I may do something similar in Excel to track how much mass I'm managing to fit in where. By adding together all of the balance weights and how far ahead of the mainwheels they are, we can see how their various effects accumulate and see how far away from the final result we actually are. I am supposed to be in London Tuesday, Wednesday and Thursday with day-job but due to administration barriers I don't have flights and accommodation booked yet so may well end up staying home. If nothing seems to happen here for the next few days, I am probably in London! 10 Link to comment Share on other sites More sharing options...
Johnny_K Posted February 17, 2019 Share Posted February 17, 2019 Are you building the model with the bomb bay doors open or closed. If they are closed you could put weight in the bomb bay. You could also put weight in the tunnel that connects the front of the plane with the rear. Unfortunately, both of these solutions will result in a shorter moment arm. 1 Link to comment Share on other sites More sharing options...
Nikolay Polyakov Posted February 17, 2019 Share Posted February 17, 2019 9 minutes ago, Jamie @ Sovereign Hobbies said: Exactly - those tongues can be drilled out so they still function, but it saves a little weight. Not much, but as the maths shows, every little bit saved at the back saves twice as much (or more) weight needed at the front It’s simple but very clever decision! Same as you: 10 minutes ago, Jamie @ Sovereign Hobbies said: I hadn't thought of that! I love your engineering solutions here, watching with interest! Cheers! 🤝 1 Link to comment Share on other sites More sharing options...
Jamie @ Sovereign Hobbies Posted February 17, 2019 Author Share Posted February 17, 2019 1 minute ago, Johnny_K said: Are you building the model with the bomb bay doors open or closed. If they are closed you could put weight in the bomb bay. You could also put weight in the tunnel that connects the front of the plane with the rear. Unfortunately, both of these solutions will result in a shorter moment arm. I'm planning on having the bomb bay closed, so that can be the back-up plan. I'm already musing that I should cut off the kit's stub axles on the main gear legs, drill through and replace those with brass rod. 1 Link to comment Share on other sites More sharing options...
pinky coffeeboat Posted February 17, 2019 Share Posted February 17, 2019 (edited) To continue to add to the weight discussion, I added nuts to the tubs for both the upper and lower forward turrets before fixing on the gun assembly and cover. Jeff Edited February 17, 2019 by pinky coffeeboat 1 Link to comment Share on other sites More sharing options...
Sturmovik Posted February 17, 2019 Share Posted February 17, 2019 1 hour ago, Jamie @ Sovereign Hobbies said: Fullsize aircraft sometimes use a weight and balance sheet with lots of component masses positioned relative to a datum point. I may do something similar in Excel to track how much mass I'm managing to fit in where. By adding together all of the balance weights and how far ahead of the mainwheels they are, we can see how their various effects accumulate and see how far away from the final result we actually are. This is exactly what I'm learning on my aircraft dispatcher course. 1 Link to comment Share on other sites More sharing options...
Brandy Posted February 18, 2019 Share Posted February 18, 2019 (edited) Nicely explained Jamie. As a pilot, my first inclination when you mentioned the weight was the same as yours, ie Dremel out the inner sides of the vertical and horizontal tail surfaces as much as possible and reduce the locating lugs. That should save quite a bit. Then add the extra plastic that can be removed from areas inside the fuselage which won't be visible when it's together and you should have a very decent weight saving. This aircraft actually helps here because of the minimal transparencies allowing very little, if anything, to be seen inside! I've never tackled anything this big, but had a similar problem with a 1:72 Nieuport IV which was notorious as a tail sitter. The kit nose was too short, so lengthening that and adding a white metal engine helped a lot, but it was replacing the tail surfaces with stock plastic sheet which made the biggest difference. Thin styrene sheet is a LOT lighter than injection moulded plastic that is also too thick! Best of luck! Ian An afterthought. Instead of drilling the tailplane locators, could you cut the centre third (or even a little more) out entirely, just leaving the fore and aft parts to locate against each other? Edited February 18, 2019 by limeypilot 3 Link to comment Share on other sites More sharing options...
Kev The Modeller Posted February 18, 2019 Share Posted February 18, 2019 Great aircraft and a very interesting build, looking forward to following this one Link to comment Share on other sites More sharing options...
amblypygid Posted February 18, 2019 Share Posted February 18, 2019 Jamie, this is a fascinating monster of a build, and I appreciate your introduction of alternate solutions to problems. That does appear to be a lot of plastic that Monogram stuffed into the rear of the airframe for little perceptible gain. Riffing on the RE magnet solution suggested earlier (which I suspect is an excellent one as you'd want a model this size to be based, right?), would it be possible to use other magnets in the tail and base to repel each other? I suspect height would be a problem, and you'd have to get the orientation spot on to avoid too much lateral force; I'd certainly balls it up, but you're an engineer! Link to comment Share on other sites More sharing options...
Ex-FAAWAFU Posted February 18, 2019 Share Posted February 18, 2019 (edited) 16 hours ago, Jamie @ Sovereign Hobbies said: Fullsize aircraft sometimes use a weight and balance sheet with lots of component masses positioned relative to a datum point. I may do something similar in Excel to track how much mass I'm managing to fit in where. By adding together all of the balance weights and how far ahead of the mainwheels they are, we can see how their various effects accumulate and see how far away from the final result we actually are. Indeed they do. The Seaking HAS5 had a significant centre of gravity issue because of the amount of extra gubbins that the RN had added during its life - pretty much all of which was well behind the original centre of gravity. If you look at a photo of an HAS1 or 2 in the hover, the fuselage is not far off level... but then we added the LAPADS table (for acoustic processing of sonobuoys) and an extra seat (complete with Aircrewman!), both of which were level with the rear half of the cargo door... so the HAS5 hovered visibly nose up and left wing low. The aircraft could handle the weight OK, but if you got it wrong you could (at least in theory - and no-one wanted to test it for real!) run out of control authority because of where that weight was. The Seaking has a number of fuel tanks distributed throughout the boat hull, so every time we prepared to go flying we had to work out the distribution of weight at various fuel states (so that we could manage the fuel and empty the tanks in a sensible order). For the same reason you will almost never see an HAS5 carrying a torpedo on the rear stations (or, if it did, then there will have been some VERY careful calculations beforehand!). We had a perspex johnson which enabled you to work out where the C of G would be at x,000 lbs of fuel, y weapons carried on z stations, and so on. The problem was solved in the HAS6, because the passive acoustics stuff was integrated into the Aircrewman’s normal sonar console, so C of G was no longer a big issue. We still managed fuel, but it wasn’t quite as critical to get it exactly right. It was never completely clear how much connexion there was, but the HAS5 also suffered from the so-called “Frame 290 crack” - frame 290 being the frame to which the rear feet of the main gearbox were attached. The Mk5 was a good ton heavier than the original design, and a lot of that weight was at the back end. Eventually even a sturdy workhorse like the Seaking starts to complain if you bolt too much on! Edited February 18, 2019 by Ex-FAAWAFU 5 Link to comment Share on other sites More sharing options...
Jamie @ Sovereign Hobbies Posted February 18, 2019 Author Share Posted February 18, 2019 2 hours ago, Ex-FAAWAFU said: Indeed they do. The Seaking HAS5 had a significant centre of gravity issue because of the amount of extra gubbins that the RN had added during its life - pretty much all of which was well behind the original centre of gravity. If you look at a photo of an HAS1 or 2 in the hover, the fuselage is not far off level... but then we added the LAPADS table (for acoustic processing of sonobuoys) and an extra seat (complete with Aircrewman!), both of which were level with the rear half of the cargo door... so the HAS5 hovered visibly nose up and left wing low. The aircraft could handle the weight OK, but if you got it wrong you could (at least in theory - and no-one wanted to test it for real!) run out of control authority because of where that weight was. The Seaking has a number of fuel tanks distributed throughout the boat hull, so every time we prepared to go flying we had to work out the distribution of weight at various fuel states (so that we could manage the fuel and empty the tanks in a sensible order). For the same reason you will almost never see an HAS5 carrying a torpedo on the rear stations (or, if it did, then there will have been some VERY careful calculations beforehand!). We had a perspex johnson which enabled you to work out where the C of G would be at x,000 lbs of fuel, y weapons carried on z stations, and so on. The problem was solved in the HAS6, because the passive acoustics stuff was integrated into the Aircrewman’s normal sonar console, so C of G was no longer a big issue. We still managed fuel, but it wasn’t quite as critical to get it exactly right. It was never completely clear how much connexion there was, but the HAS5 also suffered from the so-called “Frame 290 crack” - frame 290 being the frame to which the rear feet of the main gearbox were attached. The Mk5 was a good ton heavier than the original design, and a lot of that weight was at the back end. Eventually even a sturdy workhorse like the Seaking starts to complain if you bolt too much on! That's interesting since the longer nosed S-61N hovered nose-down. Just checking against specs and the HAS5 has a significantly higher Max TO weight than the S-61N, which surprised me actually as they fairly packed people and baggage into the latter. I guess that shows the weight of some of the military hardware! The Sikorsky HH-3E was a bit heavier than the HAS5 still but the fuselage aft of the main rotor was different so who knows what they changed inside. 4 Link to comment Share on other sites More sharing options...
Johnny_K Posted February 18, 2019 Share Posted February 18, 2019 19 hours ago, Jamie @ Sovereign Hobbies said: I'm planning on having the bomb bay closed, so that can be the back-up plan. I'm already musing that I should cut off the kit's stub axles on the main gear legs, drill through and replace those with brass rod. Are you concerned that the main gear legs will break due to the weight of the plane? The kit's gear legs are pretty sturdy. Link to comment Share on other sites More sharing options...
Jamie @ Sovereign Hobbies Posted February 18, 2019 Author Share Posted February 18, 2019 1 hour ago, Johnny_K said: Are you concerned that the main gear legs will break due to the weight of the plane? The kit's gear legs are pretty sturdy. That is a concern, particularly if the model is to go to the occassional show. Undercarriage damage from overweight models can be a plague. Mostly though, I really want a model that naturally sits on its wheels properly and I really don't want the cabin full of weights if I can possibly avoid it. I've managed to avoid going to London this week which is great news. A few minutes more with the flap wheel and this half of the tailplane is over 3 grams lighter which means 6+ grams of bulky weight avoided upfront. 3 Link to comment Share on other sites More sharing options...
Jamie @ Sovereign Hobbies Posted February 18, 2019 Author Share Posted February 18, 2019 I'm maybe not a million miles away unless I have my sums wrong... Hopefully this is now fairly self-explanatory 4 Link to comment Share on other sites More sharing options...
Pete in Lincs Posted February 18, 2019 Share Posted February 18, 2019 Undercarriage legs can be drilled down the centre and metal rods inserted. This will help with the strength and may help with the magnetism idea. 2 Link to comment Share on other sites More sharing options...
fubar57 Posted February 18, 2019 Share Posted February 18, 2019 Very interesting. Not sure if mentioned or done but if the plastic is fairly thick, the fuselage aft of the wing join could be ground out 1 Link to comment Share on other sites More sharing options...
Jamie @ Sovereign Hobbies Posted February 18, 2019 Author Share Posted February 18, 2019 I've been an idiot. I tried the nose weights in place and re-weighed the tail, then used the new residual weight on the tail for the moment and took credit for the nose-weights already in there again. I've had to re-do that. I might be able to get a bit more in at Position A2 above using lead shot instead of wheel balance weights. That will require me finding my bottle of the stuff in the big shed outside. 3 Link to comment Share on other sites More sharing options...
Jamie @ Sovereign Hobbies Posted February 18, 2019 Author Share Posted February 18, 2019 Double posted Link to comment Share on other sites More sharing options...
Johnny_K Posted February 18, 2019 Share Posted February 18, 2019 Just be careful if you decide to remove plastic from the rear of the fuselage. Revell USA no longer exists and it may be difficult to obtain a replacement fuselage if the Dremel burr burns through the plastic. If that happens, the plastic can be fixed, but that takes the fun out of modeling. One more thing to keep in mind. This a big model once finished and it takes two hands and a firm grip to pick it up. The rear of the fuselage could crack off when the model is picked up and too much plastic is removed. 2 1 Link to comment Share on other sites More sharing options...
busnproplinerfan Posted February 18, 2019 Share Posted February 18, 2019 Personally I prefer anchoring the nose wheels somehow. The landing gear is strong and SAC I think has made metal copies as well. From the ones I made it might be the way to do it. Grinding out the plastic will help a little but not enough. You could leave out the rear interior to, but with the big blisters, you may not want to. I have tought of vac forming the tail section, but I'm not the greatest at vac forming, at least nothing this big. 2 Link to comment Share on other sites More sharing options...
pinky coffeeboat Posted February 18, 2019 Share Posted February 18, 2019 My B-29 kit stood for years on its legs and didn't show any signs of bending or possibly wanting to fail. The only time the legs gave up was when in storage it was upside down and something quite heavy was slid over it shearing the main legs off (all by accident). Sadly it never made it out from storage and was scrapped a couple of years ago - after years of being moved, battered and generally abused things eventually broke off and were never recovered. Jeff 2 Link to comment Share on other sites More sharing options...
Jamie @ Sovereign Hobbies Posted February 18, 2019 Author Share Posted February 18, 2019 Fear not folks - it's going to work and it's going to be fine 😎 2 Link to comment Share on other sites More sharing options...
Uncle Uncool Posted February 18, 2019 Share Posted February 18, 2019 Jamie, How about filling the nose wheel halves with some fishing lead sink as well? I think you can get another additional 5 to 10 grams weight that way. Cheers, Unc2 2 Link to comment Share on other sites More sharing options...
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